STAMPTOOLS is a virtual circular stamp image generator with three text fields: one on top, one on the bottom, and a date sandwiched in the middle. Font style and size are independently alterable for each field, although anything outside the circle of the stamp is cropped. The color and border style of the stamp can also be changed to a limited degree.
One of the nifty features of STAMPTOOLS is its drag’n’drop compatibility with Microsoft Word, Excel, and other text-processing programs. Independent of formatting in the existing document (for most supported applications), the stamp image can be placed on any part of the page, just as a real stamp would on a finished product, and has an alpha layer (for transparency) which means it won’t obscure text it’s placed near to. There is also a “Copy to clipboard” feature for any other use of the stamp.
Sam’s Protip: If you’re looking for a way to validate documents for casual use, this could do the trick, but those looking for a way to professionally seal their documents might look into digital signatures for PDF files.